1. Field of the Invention
The present invention relates to an information register which can be loaded with data and can perform operations on those data. In particular, the information register can be used in a quantum computer or a classical computer. A classical computer is any device which processes purely classical information regardless of how advanced its technology may be, whereas a quantum computer is a device which processes quantum information (for example quantum superpositions of 0 and 1, called qubits, discussed below).
2. Description of Related Art
The field of quantum computation has been the subject of much recent research. However, to construct a practical quantum computer there are a number of requirements.
In a quantum computer, information is represented by the quantum-mechanical states of a system. In a two energy state system, the two states can represent the “basis states” 0 and 1, and such a system is known as a quantum bit or “qubit”. One requirement is that the qubit must be under precise control in order to allow the production of superposition states of the two “basis states”. Under the laws of quantum mechanics, the system can effectively be in more than one state at a particular time, and this superposition allows the qubit to represent the two individual states simultaneously. For example, in a binary mode, qubits can exist simultaneously as 0 and 1, with the probability for each state being given by a numerical coefficient.
A second requirement is that more than one of these qubits can be coupled together, such that their combined states are no longer individual qubit states, but are a combination of all the qubits together. For instance, three classical bits can form eight possible combinations: 000, 001, 010, 011, 100, 101, 110 and 111. In a coupled three-qubit system, these eight states must then be regarded as the basic states, and superpositions of all eight can be produced at the same time in a single three-qubit combination. This parallel representation of information has been shown to be highly advantageous for certain types of computer algorithms, for example factorization and searching an unordered list.
A third, very important, requirement for the successful operation of a quantum computer is that the desired states are maintained when the qubits are in real environments, i.e. where they can interact with their surroundings. In this situation they form part of a much bigger and more complex quantum system. The effect of the environment is to “decohere” the system such that the quantum computation will no longer work after a characteristic decoherence time.
Conventionally, there have been problems in providing an element, such as an information register, for a quantum computer which can meet these three requirements of single qubit control, appropriate inter-qubit interactions and small coupling to the environment.
Further problems exist with conventional computers, for example, that it is difficult to address simultaneously many bits and providing wiring to all the individual bits becomes very difficult, particularly as the size of the device is reduced.